High-frequency oscillator



Feb. 21, 1959 I CLARK HIGH-FREQUENCY OSCILLATOR 2 Sheets-Sheet 1 Filed April 30, 1946 FlG.l

FIG.2

I. In

PHI

ll Hl In! INVENTOR JAMES L. CLARK ATTORNEY Patented Feb. 21 1950 HIGH-FREQUENCY OSCILLATOR James L. Clark, Elmhurst, Ill., assignor to United States of America as represented by the Scoretary of War Application April 30, 1946, Serial No. 666,006

4 Claims. 1

This invention relates in general to electrical circuits, and more particularly to electrical oscillator circuits having a relatively wide frequency range.

Oscillators employing thermionic tubes have their frequency range limited, to a large extent, by the type of tank circuit employed. Thus, circuits with conventional coils and condensers are practical for frequencies ranging into the high frequency and very high frequency region of the electromagnetic spectrum. If a very low power output is not considered undesirable, fussiness in design and construction can be employed, which may result in the range of this type of oscillator being pushed to the higher end of the very high frequency range and into the ultra high frequency range. Frequencies at the upper end of the very high frequency range are quite often generated by circuits utilizing parallel conductor transmission lines. Such transmission lines cannot be used with efficacy in the lower end of the very high frequency region, because the lengths of the lines become excessive, and the Q of the tank circuit becomes too low.

A disadvantage of parallel conductor transmission lines as tank circuits lies in the relative awkwardness of the unit, the conductors often protruding straight out from the remainder of the oscillator a distance of several feet. Such devices often require a fairly complicated means of tuning, which is usually reflected in the overall cost of the unit.

Accordingly, among the objects of the present invention are:

1. To provide an oscillator capable of operation in the very high frequency range of the electromagnetic spectrum;

2. To provide such an oscillator having a very wide frequency range; and

3. To provide such an oscillator in which some of the disadvantages of the type of transmission line oscillators used in the prior art are absent.

In accordance with the present invention, there is provided a push-pull, plate-tuned oscillator circuit utilizing two tubes and two tank circuit v components. The tank circuit consists of two spirals of copper ribbon with a movable shorting bar used to vary the lengths of the spirals effective in producing tube oscillations. Energy is coupled from the circuit by means of a balanced coaxial line loop having a contour similar to that of the turns of the spiral coils, this balanced line feeding into a single coaxial line.

This invention will best be understood by reference to the accompanying drawings, taken in connection with the appended claims and this specification, in which:

Fig. 1 is a perspective view of an oscillator embodying the principles of the present invention;

,Fig. 2 is a top view of the oscillator of Fig. 1,

2 making clear some of the details of the structure not brought out in connection with Fig. 1;

Fig. 3 is a side view of the oscillator of Fig. 1, also accentuating some of the details of this structure not clearly shown in Fig. 1; and

Fig. 4 is a schematic circuit diagram of the oscillator of Fig. 1.

Referring now to a description of an embodiment employing the principles of the present invention and to Fig. ,1, the oscillator structure is mounted upon a flat surface I0. Upon this surface are mounted, in a symmetrical manner, two triode vacuum tubes II and I2. It is desirable that these tubes have a type of structure in which the plate lead is brought out of the top of the tube, and the grid lead is brought out of the side of the tube. One tube having a preferred type of construction and having desirable properties for use with the hereindescribed circuit is the 3024. In connection with tube II, the plate lead I3 is the only externally-projecting electrode connection that can be seen in Fig. 1. With respect to tube I2, plate lead I4 protrudes out of the top of the tube in a direction parallel to, and collinear with, the long axis thereof, and grid lead I5 extends out of the side of the tube perpendicular to the long axis thereof.

The tank circuit component associated with tube I 2 is a spirally-wound coil I6 of ribbon wire. This coil is connected to plate lead I4 through ribbon wire sections I! and I8, and has its inner end held in place by shaft 32. Feedback from the plate of tube I2 to the grid of tube II is accomplished by means of condenser 53, which consists of two coaxial cylinders, outer cylinder I9 and inner cylinder 20, with a dielectric, preferably polystyrene, positioned between them. Ribbon wire section H in the plate circuit of tube I2 is made to take the contour of the outside cylinder I9 of the feedback condenser 53 so that good contact can be achieved between these two conducting members. The inner cylinder 20 of this condenser is connected, by means of a ribbon wire 2I, to the grid lead of tube I I, this lead not being discernible in Fig. l. The condenser 53 can be made variable by moving the inner conductor along its axis, with respect to the outer conductor, by means of a suitable screw arrangement.

The tank circuit component associated with tube II is the spirally-wound coil 22, only a portion of which can be seen in Fig. 1, which is connected to the plate lead I3 through two ribbon wire sections 23 and 24, and has its inner extremity held in place by shaft 32. This spiral coil is preferably positioned so as to be substantially parallel with the spiral coil associated directly with tube I2. Section 23 is molded so a s to conform to the shape of a portion of the outer cylinder 25 of the feedback condenser 54. Con- 3 denser 54 has substantially the same physical and electrical properties as condenser 53. The inner cylinder 26 of condenser 54 is shown connected to the grid lead I of tube l2 by means of ribbon wire 21.

Movable shorting bar 28 is used to short spiral coil is to spiral coil 22, and utilizes slidable contact 29 to slide on coil it, and another slidable contact, not shown in Fig. 1, to slide on coil '22. It is desirable that these contacts be made up of a number of spring fingers, all these fingers sliding on the coil at one time, thus providing a number of parallel paths for the plate current. Shorting bar 28 has its center section transformed into a cube-shaped, hollowed-out portion 36. Into the square hole in portion 33 is fitted a square arm 35, the opposite end of this arm being securely affixed to shaft 32. Arm 3i fits into the hole in portion 3% in a tight, but slidable manner. Knob 33 is coupled directly to shaft 32, so the turning of this knob results in motion of the shorting bar 28 along spiral coils l5 and Z2. Insulating walls 3% and 3'1, made preferably of polystyrene, are used as supporting means for shaft 32.

Power is extracted from the oscillator circuit by means of an arrangement comprising a coaxial line 80, having an outer conductor fi l and an inner conductor 33, bent so as to be positioned in the near vicinity of the spiral-coil it, and a piece 35 of conducting tubing bent soas to follow the general contour of the spiral coil 22. At the tubeend of this coupling circuit, a short length of the inner conductor 38 of coaxial line 83 is exposed, and is soldered tothe end-of thetubing 35. On the other side of the spiral coils, the two sections are-brought together in a connector not shown in Fig. 1, which will be described in more detail in connection with Figs. 3 and 4.

The amount of coupling is varied by means of a shorting bar 39 which contacts the outer conductor of the coaxial line 89 by spring contact 40, and slideson the piece 35 of tubing by contact M Motion is transmitted to shorting bar '39 through arm 52 and yoke '33, which are rotated by knob 1M. A rotation of knob is does not, however, cause motion of shaft 32. Both arm 42 and yoke 83, consisting of cross-bar 43a. and side bars 832) and 30, are constructed of an insulating'material. Shielded box 45 may be employed to house components of circuits auxiliary to the oscillator proper.

Fig. 2 is a top view of the arrangement of Fig. 1, and is presented here to bring out details not emphasized in the showing of Fig. 1. The symmetrical nature of the structure will be evident from Fig. 2. The end view of the plate leads l3 and i l of tubes H and [2, respectively, may be seen, and it will be noted that the grid leads 46 and 5-5, respectively, of these tubes are positioned so as to be symmetrical with respect to one another. In the tank circuit component associated with tube l2, which consists of the combination of spiral coil I6, section ll, and section 18, all of ribbon wire, it is desirable to have the least number of soldered joints practicable. To this end, one embodiment of this structure utilizes coil l6 and section ll of one piece of wire, while section it is another piece soldered onto section H, this arrangement being employed because of the-sharp bend in the wire between the two latter-mentioned pieces. One end of ribbon wire 58 is wrapped securely around plate lead It. The construction of the tank circuit component associated with tube H, consisting of the combination of spiral coil 22, section 23 and section 24, can also be more clearly observed with reference to Fig. 2. The shorting bar 23, used to determine the lengths of the spiral coils that are to be efiective as the oscillator tank circuit, makes contact with the two coils l6 and 22 by means of slidable fingers 29 and ll, respectively. This shorting bar has motion transmitted directly to its center portion :30 through arm 3|, shaft 32, and knob 33.

The ribbon wire 2'! connecting the grid lead 3.5. of tube 92. .to the inner cylinder 26 of plate feedback condenser 54 is given a quarter twist, as shown. A similar twist is given to ribbon wire r 24 which couples the grid lead 46 of tube H to the inner cylinder 20 of the condenser 53.

The output coupling arrangement consists of a coaxial line 8% with an'outerconductor '34 and an inner conductor 38, and a piece of conducting tubing 25, oneend of the inner conductor SBbeing soldered to the wallof theoonducting tubing 26 at the termination thereof. The-shorting bar 39, used to fix the effective length of the two halves of the coupling loop,mak-es contact with the tubing 24 through the spring, triangularshaped loop 4!, and with outer conductor 34 through the spring, triangular-shaped loop 40. Motionis transmitted'to shorting bar 38 through arm 42, yoke 43 and knob EL Insulating wallstli and 31 are used to support the shafts leasing from knob 33 and knob a l, and base it isused to support theentire assembly.

The means of connecting tubing 24 to coaxial line Bil which is positioned at the back end of the structure, is omitted from Fig. 2 for the sake of clarity.

Further detailsof the arrangementof the present embodimennespecially relative-to thespiral coils and the outputsection of the output coupling members, willbecome apparent by reference to Fig. 3. Several-portions of the structure are omitted in this drawing, in order to make the features desired toab-estressed in this'figure stand outmoredistinctly. Only-one (l2) oft'he tubes is shown, with itsplate lead 'M' and its grid lead [5. A portion of the end of the. grid ribbon wire it can be observed. A side view .of the plate tank circuit component, comprisingthecombination of section [3 connecting to plate lead I l, section H and spiral .coil :l-6, brings out the design of the spiral and the method of connecting this structure to shaft 3,2. 'It will be noted that section E? is made to. follow .thecontour of a portion of the outer cylinder l-Q of the feedback condenser 53. The outer conductor :31! of the coaxial line portion ofthe output coupling structure is seen 'to .follow the approximate contour of the spiralcoil l5, thecoaxial line terminating in connectorB'. The outlines of yoke lfi and of arm '34 are discernible, as are wall members 31 and base l0.

Fig. 4 is a schematic-circuit diagram of this particular embodiment. The circuit will be seen to be a push-pull, plate-tuned oscillator circuit. The tank circuit, comprising transmission lines in the form of spirally-shaped coils, consists of line 50, which represents the series combination of ribbon wire sections I6, I! and I8, and which is connected to the plate of tube l2, and line 5!, which represents the-series combinationof ribbon wire sections 22, 23, and 24, and which is connected to the plate of tube I! l. Slidable connector 52, which is movablealong lines '50 andBl, represents shortingbarZB-incOmbinatiOn with spring fingers 29 and 41. The mid-point of the shorting member 52 is joined to the connecting point of lines 50 and i by connection 8!, because coils l6 and 22 terminate on shaft 32, as does the arm 31 leading from shorting bar 28. The schematic drawin of the output coupling arrangement is in substantially the same detail as is the actual structure. The half loop of tubing 35 is grounded at one point along its length, is soldered to the outer conductor 34 of the coaxial line 80 at one end, and is soldered to the inner conductor 38 of the coaxial line 80 at its other end. The plate of tube I2 is connected to the grid of tube H through condenser 53, which represents the feedback condenser consisting of cylindrical plates l9 and 20. Similarly, the plate of tube H is connected to the grid of the tube l2 through condenser 54, which represents the feedback condenser comprising cylindrical plates 25 and 26.

In the filament leads of tube l2, choke coils and 56, are placed and are returned to ground through condensers 51 and 58, respectively. The choke coils 59 and 60 in the filament leads of tube II are also connected to condensers 51 and 58, respectively. The filament current is fed to these tubes, in parallel, through leads 6| and 52 from a suitable source (not shown). The grid of tube II is connected to a common point 55 through resistor 63 and coil 54, while the grid of tube I2 is connected to the point 65 through resistor 66 and coil 61. This common point is connected to ground through coil 68, resistor $9 and the meter circuit comprising condenser Iii, rheostat H and ammeter 12.

The operation of the described embodiment of the present invention will now be discussed. It will be noted that the spiral coil tank circuit is essentially a combination of a transmission line tank circuit and an inductive coil tank ,1

circuit. The length of the plate current path is made to be great enough so that it is an appreciable fraction of a wavelength, which gives it som of the characteristics of a transmission line type of tank circuit. The spiral form that the lines take, however, causes an increased inductance over that of a straight-wire transmission line circuit, and so provides the additive effect of a coil type of tank circuit. The tuning characteristic that this circuit was found to have is between that of a conventional coil type and a transmission line type of circuit.

The tank circuit is tuned by varying the effective length of the spiral coils by means of the shorting bar. The resonant frequency is thus fixed by the length of the coils in wavelengths together with the added effect of the inductance between turns in the spiral.

With this circuit, a relatively very wide frequency range may be obtained, one configuration in practice providing a range between 60 and 325 megacycles, with a radio frequency power output varying from 50 to 25 watts as the frequency increases over this region. As the low frequency end of the range is approached, i. e., as the shorting bar 28 is moved away from the plate leads, it is believed at this time, with the spiral tank, that the distributed capacitance increases relatively slowly with respect to the inductance, with the result being a wide band of output frequencies. Besides providing a relatively wide frequency range, this type of spiral coil tank circuit results in a smaller, more compact unit than that used in the prior type of transmission line oscillator. The tuning mechathe center conductor of the coaxial line.

nism for the present circuit can also be made relatively compact.

Ribbon wire in plate and grid circuits is set forth here as a preferable type of conductor to use. Other types of conducting means may be employed but, in general, the results may not be as satisfactory as those obtained with the use of ribbon wire. A primary purpose in using ribbon wire over the conventional type of wire is the increased surface area of the ribbon type. An increased surface area means a decreased resistance to current flow, since, at the frequencies at which the oscillator in the one embodiment is intended to operate, the current flows through a thin surface sheath of conductor and, hence, a higher Q and a greater stability for the circuit may be obtained. Ribbon wire also allows the effective use of multiple contact fingers 29 and 41, providing a relatively low inductance path at this point in the circuit, the point of maximum radio frequency current. The smaller this contact inductance, the higher will be the upper frequency range of the oscillator. The use of tubing for conductor 35 is also preferable because of its lower resistive properties.

Condensers 53 and 54 should be very small, because of the relatively high frequencies involved. One effective way of providing these low capacitances is to construct the condenser of two coaxial cylinders between which is positioned a dielectric such as polystyrene. This may provide a small, easily variable capacitance.

The particular type of output coupling described here was chosen because of its property of transforming from a balanced to an unbalanced type of circuit. Since the present circuit is a push-pull oscillator, the electromagnetic field emanating from one spiral coil is, at any instant, out of phase with the electromagnetic field from the other coil. To couple energy from both of these fields at the same time, this type of coaxial line-single conductor type of coupling is desirable. It can be seen that the tubing, which receives energy from one coil, is connected to The outer conductor of this coaxial line, however, receives energy from the other coil, and so is 180 out of phase with the center conductor, thus achieving the result desired. In general, it may be said that the connections in this circuit are such that the energy induced in one side of the coupler reinforces the energy induced in the other side. The effective mutual inductance between the plate coils and the output coupling loop is varied by changing the position of the shorting bar 39, thus varying the amount of coupling to the output circuit. Coupling is at a maximum when the shorting bar is at the grounded end of the loop.

Referring now to the circuit diagram of Fig. 4, it is observed that the tank circuit, essentially comprising transmission lines 50 and 5|, is connected not only between the plates of the two tubes, but also between plate and grid of each tube, condensers 53 and 54 being used as low impedance paths in this respect. The push-pull effect, therefore, can be clearly seen. Another purpose of condensers 53 and 54 is to help to provide the bias voltage for the two tubes. These condensers can be easily charged from the positive voltage sources connected to the plates, when the grids of the tubes go positive, but must discharge through resistors 69 and either 63 or 66, thus providing a relatively long time constant discharge path. The average flow of current 3? through: these resistors" provides ".bias ti011'13h8 ztwo tubes. The meter 12 is used togiveanvindication of grid current flow from -..both .tubes.

It may be desirablev to provide. a single-knob tuning arrangement, whereby the output power varies in a, predetermined manner. pThisican be accomplished by gearing the axle about which yoke 43iturns and shaft 32. -to thegsingleknob.

While there has been described WhatilS atgpresent considered to be the preferred -.embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications .may be made therein: without departing from the spirit of the invention, and itis, therefore, intendedto coveriall such changes and modifications. as fall within the true spirit and scope of the invention.

What is claimed is:

1. In combination, a push-pull variable frequency electronic oscillator, a first thermionic tube, a second thermionic tube, a tank circuit comprising a first and a second coil,-said first coilbeing associated directlywithsaid first tube, said second coil being associated directly with said second tube, each of 'said coils having a spiral shape, thelengths of said coils being an-appreciable fraction of the operating wavelength, first movable short-circuiting:means connecting said first and saidsecond coils, whereby movement of saidxfirst short-circuiting :means varies the, electrical length of said coils, means for feeding-energy back fromsai'djfirst'tubeto said second tube and fromisaid second tubevtosaidffirst tube; \and an -adjustable'output meanscomprising a coaxial :line having an inner conductor-and an outer conductor 'saidlouter conductor being positioned nearsaid'iirst .coil and'having a shape similar to that of: the outside :loopof said first coil, a'single wire conductor .positionednear'said second coil andhaving a shapesimilar tothatoftheoutside loop .of saidsecond coil, one end of said single Wireconductor being connected to the innerconductor of said coaxialline'atta first point oncsaid coaxialdine, the other end of saidsingle wire conductor being connected to the outer conductor of said coaxial line at a second'pointon: said coaxial line, and second movable sh'ort-circuiting means for adjusting'the electrical length of said output means.

2. A high frequency. oscillator'of compact size and wide tuning range oonrprising'a chassis, a first electron discharge device, a second: electron discharge device, each of said :dev-ices having. an anode, a cathode andaa controhgrid, said devices being mounted-adjacent to eachother, a pair of opposingwalls verticallymounted.uponsaid chassis, a rotatable shaft extending between and through said walls, first andsecondispiralzribbon conductors centrally disposed about said shaft between said verticalwalls, eachaof said conductors connected to an anode of said dischargedevices, .a rod mounted upon said shaft, .av crossing member adapted for slidable longitudinal movement-alon said rod, said crossing member having contact means for engagingisaid spiral conductorswhereby said conductors will be: electrically connected, means'forrotating said shaft. to adjuSt'the'poSition of said. crossing member thereby varying thelelectrical length of said spiral conductors, adjustable output means comprising coaxial transmission line-having an outer and inner-com ductor, said outer conductor being-disposed concentrically with saidfirst spiral conductor, .said

inner aconductor "being extended, and said extendedportion being disposed concentricallywith said second spiral conductor, a yoke straddling said coaxial line andsup-ported at two points external of said vertical walls, said yoke having shorting means. cooperating with said inner and outer conductors, and means for rotating said yoke to move saidshortingmeans along said coaxial .line whereby the coupling will be adjusted.

3. A variable frequency oscillator comprising a chassis, .first'and second vacuum tubes, each of said vacuum tubes having at least an anode, cathode'and control. grid, said first and second vacuum tubes being mounted adjacent to each other, a pairnoi opposing walls vertically mounted on said chassis, a rotatable shaft extending between and throughsaid walls, first andsecond spiral ribbon conductors centrallydisposed about said shaft between said vertical walls, each of said conductors being connected to an anodeof said vacuum tubes, a rod mounted upon said shaft, a crossing member mounted for slidable longitudinal movement along said rod, said crossing member having contact means for engaging said spiral conductors whereby said conductors will be electrically connected, means for rotating said shaft to adjust'the position of said crossing member whereby the electrical length of said spiral conductors will be adjusted, first and second capacitors mounted on said walls and connected to feed back energy to sustain oscillations insaid oscillator, adjustable output means comprising a coaxial line having an inner conductor and outer conductor, said conductor being disposed adjacent to one of said spiral conductors, said inner conductor beingextendedand said extended sec tion being disposed adjacent to theother of said spiral conductors, a yoke. supported on said shaft at points external of said verticalwalls, shorting means mounted upon said yoke comprising an inwardly extending member and a crossingmember having contact means for electrically. shorting said outer and innerconductors.

4. Ina variable frequency oscillator structure having a pair of-spirally woundconductors form- 60 ing-said outer and inner conductors.

JAIWES L. CLARK.

REFERENCES .CHTED 5 The following references are of record in the file of this patent:

UNITED SYFATES PATENTS Number Name Date 70 1,389,255 McDonald Aug. 30, 1921 2,126,541 De Forest Aug. 9, 1938 2,160,655 Hansell May 30, 1939 2,292,254 VanBeuren Aug. 4, 1942 Certificate of Correction Patent N 0. 2,498,529 February 21, 1950 JAMES L. CLARK It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 34, before conductor, second occurrence, insert outer;

and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of July, A. D. 1950.

THOMAS F. MURPHY,

Assistant Gammz'ssz'oner of Patents.

Certificate of Correction Patent No. 2,498,529 February 21, 1950 JAMES L. CLARK It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8 line 34 before conductor second occurrence insert outer 1 7 7 7 and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 25th day of July, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

